Surface mount packages containing semiconductor chips and other electronic devices include electrical contacts for electrical coupling to a substrate, such as a printed circuit board. Frequently, a quantity of solder is placed on one or more of the electrical contacts to form solder joints that accomplish the electrical coupling. For surface mount packages utilizing solder joints in this way, solder joint reliability is an important design issue. Larger solder joints tend to be more robust and to last longer than smaller solder joints; so for solder joint reliability, larger solder joints are preferred. However, larger solder joints require larger electrical contacts on which to place the solder joints, and larger electrical contacts lead to larger packages that are less cost-effective and less competitive.
The size of the electrical contacts, as well as their pitch, is dictated by the thickness of the leadframe and by the etch process used to produce the desired pattern in the leadframe. Thicker leadframes require larger electrical contacts. Surface mount packages, such as a power quad flat non-leaded (QFN) package, designed for high power applications must be relatively thick in order to support the thermal requirements of the high power application. In conventional leadframe technology, these thick leadframes lead to low solder joint reliability, large, inefficient package sizes, or both. Accordingly, a need exists for a cost-effective, efficient leadframe having electrical contacts that are closely spaced and that offer good solder joint reliability.
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. The same reference numerals in different figures denote the same elements.
The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms “comprise,” “include,” “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under, ” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. The term “coupled,” as used herein, is defined as directly or indirectly connected in an electrical or non-electrical manner.